A lithium-ion secondary battery uses a lithium transition-metal oxide as an active material of a positive electrode, carbon as an active material of a negative electrode, and a non-aqueous electrolyte solution obtained by dissolving lithium salt in an organic solvent as an electrolyte. In recent years, such a lithium-ion secondary battery has been broadly used in small-sized devices such as portable telephones and notebook-type personal computers. An application of such a secondary battery to large-scale devices, e.g., to in-car power supplies for hybrid cars, plug-in hybrid cars, electric cars, and the like, and a fixed power supply for power storage or the like, has been considered.
When the common lithium-ion secondary battery is applied to large-sized equipment, it is important to increase the battery in safety. The lithium-ion secondary battery is likely to leak a liquid and generate gas because it employs a non-aqueous electrolyte solution.